Glaucoma implant

ABSTRACT

An implant for use in the treatment of glaucoma is disclosed wherein the implant comprises an elastomeric plate having a non-valved elastomeric drainage tube attached thereto. The plate is elliptical in shape and curved so as to conform to the curvature of the eye. The plate is inserted into the eye in an incision made in the Tenon&#39;s capsule and sutured to the sclera. The drainage tube is tunnelled through the Tenon&#39;s capsule and cornea and inserted into the anterior chamber, thus providing patent fluid communication between the anterior chamber and the elastomeric plate. The flexible structure of the plate allows the plate to be easily inserted, thus reducing the surgical procedure length. In addition, the pliable material minimizes th risk of damage and trauma to surrounding tissues in the insertion process.

FIELD OF THE INVENTION

The invention relates to ocular implants, and, in particular, to animplant used in the treatment of glaucoma.

BACKGROUND OF THE INVENTION

Aqueous is a clear, colorless fluid that fills the anterior andposterior chambers of the eye. The aqueous is formed by the ciliary bodyin the eye and is a carrier of nutrients for the lens. In addition, theaqueous provides a continuous stream into which surrounding tissues candischarge the waste products of metabolism.

The aqueous produced in the ciliary processes circulates from theposterior chamber to the anterior chamber of the eye through the pupiland is absorbed through the trabecular meshwork, a plurality ofcrisscrossing collagen cords covered by endothelium. Once through thetrabecular meshwork, the aqueous passes through Schlemm's canal and intovenous circulation. The rate of aqeuous outflow through the trabecularmeshwork in a normal eye is typically 2.1 μL/min. Intraocular pressurein the eye is maintained by the formation and drainage of the aqueous.All the tissues within the corneoscleral coat covering the eyeball aresubject to this pressure, which is higher than pressure exerted ontissues at other locations in the body.

Glaucoma is a progressive disease of the eye characterized by a gradualincrease of intraocular pressure. This increase in pressure is mostcommonly caused by stenosis or blockage of the aqueous outflow channel,resulting in excessive buildup of aqueous fluid in the eyeball. Othercauses include increase in venous pressure outside the eye which isreflected back through the aqueous drainage channels and increasedproduction of aqueous. In a "normal" eye, intraocular pressure rangesfrom 4 to 12 mm mercury. In an eye with glaucoma, this pressure can riseto as much as 50 mm mercury. This increase in intraocular pressureproduces gradual and permanent loss of vision in the afflicted eye.

Existing corrective methods for the treatment of glaucoma include drugs,surgery, and implants. Miotic drugs lower intraocular pressure byfacilitating aqueous outflow. Beta blockers, epinephrine products, andcarbonic anhydrase inhibitors which inhibit production of the aqueous,are also commonly used in pharmacological glaucoma treatment. Steroidshave been used in long-term glaucoma treatment as well. However,pharmacological treatment is prohibitively expensive to a large majorityof glaucoma patients. In addition, many people afflicted with thedisease live in remote or undeveloped areas where the drugs are notreadily accessible. The drugs used in the treatment, in particular thesteroids, often have undesirable side effects and many of the long-termeffects resulting from prolonged use are not yet known.

Surgical procedures have been developed in an effort to treat victims ofglaucoma. An iridectomy, removal of a portion of the iris, is often usedin angle-closure glaucoma wherein there is an occlusion of thetrabecular meshwork by iris contact. Removal of a piece of the iris thengives the aqueous free passage from the posterior to the anteriorchambers in the eye. A trabeculotomy, opening the inner wall ofSchlemm's canal, is often performed in cases of open-angle glaucoma soas to increase the outflow of the aqueous, thereby decreasingintraocular pressure. While often successful, these surgical techniquespossess inherent risks associated with invasive surgery on an alreadyafflicted eye. Furthermore, the tissue of the eye can grow back to thepre-operative condition, thereby necessitating the need for furthertreatment.

Ocular implants are often used in long-term glaucoma treatment withoutthe disadvantages of drugs and invasive surgery. One such implant isdisclosed in U.S. Pat. No. 4,457,757 entitled "Device for DrainingAqueous Humor" and commercially available as the Molteno™ Seton Implant.The implant comprises a drainage tube connected to one or more ridgedplate reservoirs. The reservoir plates are designed to conform to thecurvature of the eye. A reservoir plate is placed under Tenon's capsuleand sutured to the sclera. The drainage tube is implanted into theanterior chamber through a scleral flap. A second plate can be implantedunder the superior rectus muscle and sutured to the sclera. At thispoint, the body will form a tissue around these plates. Increasedpressure causes the tissues above the plates to lift and form a blebinto which aqueous fluid from the anterior chamber drains via thedrainage tube. Once inside the bleb, the aqeuous seeps intointercellular spaces and is removed by surrounding capillaries orlymhpatics. This type of implant is disadvantageous as the plates areformed of a rigid plastic which makes insertion beneath the eye tissuedifficult and time-consuming. Furthermore, the rigid material poses arisk of irritation and/or damage to adjacent vasculature and tissue.

UK Patent Application 2,160,778 entitled "Aqueous humor drainage device"discloses a similar type of implant device comprising a drainage tubeand a drainage body. The tube is fixed to and opens directly onto asurface of the body. The device is sutured to the sclera of the eye andthe tube positioned within the anterior chamber so as to provide outflowfor the aqueous contained therein. The device further includes apressure gradient limiting valve formed as a slit in the tube, however,this type of valve does not allow patent, i.e., open or two-way, flowthrough the drainage tube, thereby preventing retrograde aqueous flowinto the anterior chamber.

SUMMARY OF THE INVENTION

The present invention provides an implant for the treatment of glaucomawhich can be easily inserted into an afflicted eye and which providesfor patent flow between the implant and the anterior chamber of the eye.The implant comprises a single plate formed of a pliable, elastomericmaterial having a non-valved tube attached to and opening onto the uppersurface of the plate. The pliable plate is sutured to the sclera andcovered by a thick flap of Tenon's capsule so as to be encapsulatedwithin a drainage bleb. The attached tube is tunneled out throughTenon's capsule and in through the limbus so as to provide a drain foraqueous fluid. The exposed portion of the tube is covered by a scleralgraft. Because of the pliable construction and shape, the device can beimplanted much quicker than previously realized with other implants.This substantially shortens the time required to perform the surgicalprocedure.

In a unique aspect of the invention, the plate is constructed so as tobe radio-opaque. This allows the implant to be easily viewed by X-rayafter surgery, advantageously allowing progress monitoring. A suture isplaced around the drainage tube and knotted to close off the tube andprevent initial flow between the anterior chamber and elastomeric plate.Once bleb tissue formation is complete the suture is removed in a secondsurgical procedure. Alternatively, a dissolving suture can be used tosecure the drainage tube.

In an alternative embodiment, the device includes a dissolving plugcontained within the drainage tube. The plug prevents the drainage ofaqueous fluid until formation of the bleb is completed. Once blebformation has occurred, the plug dissolves, allowing for unrestrictedflow between the anterior chamber and bleb. Additional alternativeembodiments are disclosed wherein the drainage tube comprises doublelumen tubing having a primary lumen and a substantially smallersecondary lumen. The primary lumen is provided with a dissolving plugwhich prevents aqueous flow until bleb formation is complete. Thesecondary lumen is provided with a flow restrictor or valve to allowinitial flow between the anterior chamber and bleb. In a furtheralternative embodiment, the drainage tube comprises first and secondparallel drainage tubes fitted with a dissolving plug and flowrestrictor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view taken vertically through the upper, frontalportion of the eye, and FIG. 2 is a schematic, perspective view of theeye, both illustrating the present invention implanted in a human eye;

FIG. 3 and FIG. 4 are perspective views illustrating the implant of thepresent invention;

FIG. 5 is an alternative embodiment of the drainage tube;

FIGS. 5a through 5d are cross-sectional views illustrating variousconfigurations of the drainage tube of FIG. 5;

FIG. 6 shows an additional alternative embodiment of the presentinvention;

FIG. 7 illustrates a further embodiment of the implant.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 and FIG. 2 illustrate an implant 10 constructed in accordancewith the present invention positioned within the tissue of an eye 12.The relevant structure of the eye 12 will be described briefly below soas to provide background for the anatomical terms incorporated herein,however, it should be realized that several anatomical details have beenomitted for clarity of understanding. The tough outer membrane known asthe sclera 14 covers all of the eye 12 except that portion covered bythe cornea 16, the thin, transparent membrane which covers the iris 18and the pupil 20. The cornea 16 merges into the sclera 14 at a juncturereferred to as the limbus 22. The ciliary body 26 begins at the limbus22 and extends along the interior of the sclera 14 and becomes thechoroid 28. The choroid 28 is a vascular membrane which extends alongthe retina back toward the optic nerve.

It is well-known that aqueous is produced by the ciliary body 26 andreaches the anterior chamber 30 formed between the iris 18 and thecornea 16 through the pupil 20. In a normal eye, the aqueous is removedthrough the trabecular meshwork 32. There the aqueous passes throughSchlemm's canal 36 and through veins which merge with blood-carryingveins and into venous circulation. Intraocular pressure is maintained inthe eye 12 by the intricate balance of secretion and absorption oroutflow of the aqueous in the manner described above. Glaucoma resultsfrom excessive buildup of aqueous fluid in the anterior chamber 30 whichproduces an increase in intraocular pressure.

The present invention is designed for treatment of glaucoma byfacilitating the outflow of the aqueous in the anterior chamber 30 ofthe eye 12. The implant 10 comprises a pliable carrier plate 40connected to a drainage tube 42. As illustrated in FIG. 1, the carrierplate 40 is implanted in the eye 12 beneath a layer of Tenon's capsule44 and sutured to the sclera 14. The discharge tube 42 comprises a firstend 46 a second end 48 wherein the first end 46 is attached to the plate40. The second end 48 of the tube 42 extends through the layer ofTenon's capsule 44 and through the cornea 16 into the anterior chamber30 of the eye 12. A scleral graft 50 covers the exposed portion of thetube 42 located between the Tenon's capsule 44 and the cornea 16. Alarge drainage bleb 52 surrounds the carrier plate 40 and lifts thelayer of Tenon's capsule 44 above the sclera 14.

The implant 10 is shown in more detail in FIG. 2 and FIG. 3. The carrierplate 40 is generally spherical in shape, and has a perimeter which iselliptical. The surface area of the plate 40 is preferably in the rangeof 100 to 600 mm² depending on glaucoma condition and the radius ofcurvature of the plate is preferably 12 to 14 mm. The carrier plate 40includes a raised ridge 56 formed adjacent one of the larger-radiusperimeter edges of the ellipse, on the convex spherical surface. Therounded edge of the plate 40 extending on either side of the raisedridge 56, not including that portion of the plate 40 adjacent the ridge56, is entirely radiused, tapered, and blended so as to facilitateinsertion as described below. The inner surface of the carrier plate 40is concave so as to conform to the curvature of the eye 12 and thecurvature of the ridge 56 matches the curvature of the sclera 14. Anextension 58 of the carrier plate 40 is formed adjacent the ridge 56 andincludes two small suture holes 60, 62. The thickness of the plate 40 ispreferably in the range of 0.5 to 2.0 mm.

The drainage tube 42 is connected to the carrier plate 40 with adhesive,such as Clear Silicone Rubber Adhesive RTV-118 manufactured by GeneralElectric Silicone Products of Waterford, N.Y., via a small hole 64formed in the ridge 56 and is bonded to the plate 40 using well-knownbonding techniques. The first end of the tube 46 thus drains into therecess formed at the junction of the ridge 56 and the smooth outersurface of the carrier plate 40. The plate 40 is preferably formed ofsilicone elastomer, such as SILASTIC™, Medical Grade Q7-4765, 65 ShoreA, manufactured by Dow Corning Corporation of Midland, Mich., althoughother silicone elastomers in the range of 40-85 Shore A and having goodelastic memory are also suitable. The silicone elastomer is filled witha radiopaque material, such as Barium Sulfate, so that the implant isvisible in X-ray procedures, thereby allowing patient progressmonitoring. The drainage tube 42 is preferably a 1.0 to 3.0 French flowtube, approximately 10 mm in length, formed of SILASTIC™, Medical GradeRX-50, also available from Dow Corning Corporation.

The present invention can be implanted using known opthalmologicalsurgical techniques and, with reference to FIG. 1 and FIG. 4, thesurgical implant procedure will be briefly described. An initialincision 70 is made in the Tenon's capsule 44 proximal the limbus 22.The carrier plate 40 is inserted through this incision 70 and positionedbeneath the Tenon's capsule 44 and a portion of the rectus muscle 72,thus covering the sclera 14. The carrier plate 40 can be sutured to thesclera 14, or alternatively, to the rectus muscle 72 if a larger implant10 is used, with the suture holes 60, 62. The drainage tube 42 istunneled out through the Tenon's capsule 44 and in through the limbus 22such that the second end 48 of the tube 42 extends into the anteriorchamber 30 of the eye 12. The exposed portion of the drainage tube 42 isthen covered with the scleral graft 50. The drainage tube 42 is suturedclosed with a suture(s) 74 to prevent any drainage of aqueous prior toformation of the bleb tissue 52 over the carrier plate 40.

The formation of the bleb 52 occurs in response to the introduction ofthe carrier plate 40 into the tissue of the eye 12. The bleb 52comprises a thin layer of connective tissue which encapsulates thecarrier plate 40, thus lifting the Tenon's capsule 44 above the sclera14 as shown. Typically, bleb formation occurs in the range of 2 to 8weeks postoperatively, at which time additional surgery can be performedto remove the suture 74 and allow flow of aqueous from the anteriorchamber 30 to the bleb 52 via the drainage tube 42. Alternatively, adissolving suture can be used to seal the drainage tube 42. Afterremoval or dissolution of the suture 74 blocking the drainage tube 42,the aqueous flow between the tube 42 and bleb 52 is advantageously apatent flow, allowing for both flow from the anterior chamber 30 to thebleb 52 and vice versa. This ensures that retrograde flow from the bleb52 to the anterior chamber 30, occurring in response to pressure on theeye 12 from the outside, for example, when the lid is forced closed orwhen the eyeball is pressed on with a finger, does not adversely orharmfully affect intraocular pressure within the eye 12. The fluidcontained in the bleb 52 seeps through the bleb into intracellularspaces within eye 12 and is then removed through surrounding capillariesor lymphatics.

The flexible, elastomeric material used to form the present inventionand its elliptical shape allow the implant 10 to be inserted much moreeasily than previously realized with other glaucoma treatment implants.During the insertion process, the carrier plate 40 can be "folded" inhalf about the axis of the tube 42 and then inserted through theincision 70. Once placed through the incision 70, the carrier plate 40will return to its original shape and can be positioned so as to coverthe sclera 14, as described above. Further, the material from which theplate 40 is formed is soft and pliable, which results in much lesstrauma and irritation to the surrounding tissues and vasculature thanexperienced with a rigid plate device. In addition, since the plate 40is folded, a smaller incision can be made in the Tenon's capsule 44.Thus, the pliable carrier plate 40 significantly decreases the surgicalprocedure length while also minimizing tissue and vasculature damagewhich can occur in the insertion process.

In an alternative embodiment illustrated in FIG. 5, the drainage tube 42is formed as double lumen tubing having a primary lumen 80 and asecondary lumen 82 substantially smaller than the primary lumen 80. Adissolving plug 84 is placed within the primary lumen 80 to ensure thatthe majority of aqueous flow does not begin until formation of the bleb52 is complete. The secondary lumen 82 is provided with a flowrestrictor, small valve, or filter 86 which allows for a small amount ofinitial aqueous flow during bleb formation. The dissolving plug 84 ispreferably formed of Poly Vinyl Alcohol (PVA), Poly Vinyl Pyrolidone(PVP), enzymatically activated collagen, or other biomedically suitablematerials which slowly dissolve, thus gradually permitting the flow ofaqueous and relieving intraocular pressure. As shown in FIGS. 5a through5d, a variety of primary and secondary lumen 80, 82 configurations arepossible. Although four configurations are illustrated, one skilled inthe art will recognize that various other embodiments could beconstructed.

Another alternative embodiment of the present invention is illustratedin FIG. 6. FIG. 6 illustrates an implant 88 having a carrier plate 40, araised ridge 56, a plate extension 58, and suture holes 60, 62,essentially identical to that disclosed and shown in FIGS. 2 and 3 andnumbered correspondingly. The implant 88 is attached to the eye 12 inthe same manner as shown in FIGS. 1 and 4 so as to provide aqueous flowbetween the anterior chamber 30 and bleb 52. The implant 88 includesfirst and second parallel drainage tubes 90, 92 positioned adjacent thesuture holes 60, 62 and bonded to the raised ridge 56. The firstdischarge tube 60 is fitted with a dissolving plug 94 which slowlydissolves to provide gradual flow from the anterior chamber 30 to thebleb 52. As described above, the plug 94 is formed of a polymericmaterial such as PVP, PVA, or collagen. Alternatively, a ligature couldbe used to secure the first tube 90 and control flow between theanterior chamber 30 and bleb 52. A micron filter or flow restrictor 96is contained within the second discharge tube 62 to provide a relativelysmall amount of initial flow between the anterior chamber 30 and bleb52.

A further alternative embodiment of the invention is illustrated in FIG.7 wherein first and second discharge tubes 100, 102, are oriented in a"Y" configuration and merge into a single discharge tube 104 whose end106 is placed inside the anterior chamber 30. As in the embodimentdescribed above and illustrated in FIG. 6, the first discharge tube 100includes a dissolving plug 94 and the second discharge tube includes aflow restrictor or valve 96 placed therein. In this manner, aqueous flowis controlled until formation of the bleb 52 is complete.

Although the invention has been described with reference to specificembodiments, the description is intended to be illustrative of theinvention and is not intended to be limiting. Various modifications andapplications may occur to those skilled in the art without departingfrom the true spirit and scope of the invention as defined in theappended claims.

What is claimed is:
 1. An implant for draining aqueous fluid from aneye, comprising:a thin, elastomeric plate having first and secondsurfaces joined at the plate perimeter, said perimeter of said platebeing elliptical, said first and second surfaces curved spherically toconform to the curvature of said eye; and an elastomeric drainage tubeattached to said plate, said drainage tube comprising a first end and asecond end, said first end open onto one of said first and secondsurfaces of said elastomeric plate and wherein said second end extendsfor connection with said eye to provide fluid communication between saideye and said one of said first and second surfaces of said elastomericplate, wherein said drainage tube includes a dissolving plug positionedtherein, said dissolving plug for controlling said flow between said eyeand one of said first and second surfaces of said elastomeric plate. 2.An implant for draining aqueous fluid from an eye, comprising:a thin,elastomeric plate having first and second surfaces joined at the plateperimeter, said perimeter of said plate being elliptical, said first andsecond surfaces curved spherically to conform to the curvature of saideye; and an elastomeric drainage tube attached to said plate, saiddrainage tube comprising a first end and a second end, said first endopen onto one of said first and second surfaces of said elastomericplate and wherein said second end extends for connection with said eyeto provide fluid communication between said eye and said one of saidfirst and second surfaces of said elastomeric plate, wherein saiddrainage tube includes a dissolving plug positioned therein, saiddissolving plug for controlling said flow between said eye and one ofsaid first and second surfaces of said elastomeric plate, wherein saiddrainage tube further comprises a secondary lumen having diametersmaller than the diameter of said discharge tube, said secondary lumenfor providing initial flow between said eye and one of said first andsecond surfaces of said elastomeric plate.
 3. An implant for drainingaqueous fluid from an eye, comprising:a thin, elastomeric plate havingfirst and second surfaces joined at the plate perimeter, said perimeterof said plate being elliptical, said first and second surfaces curvedspherically to conform to the curvature of said eye; and an elastomericdrainage tube attached to said plate, said drainage tube comprising afirst end and a second end, said first end open onto one of said firstand second surfaces of said elastomeric plate and wherein said secondend extends for connection with said eye to provide fluid communicationbetween said eye and said one of said first and second surfaces of saidelastomeric plate, wherein said drainage tube comprises first and seconddrainage tubes, said first drainage tube having a dissolving plugpositioned therein, said second drainage tube having a flow restrictorpositioned therein, wherein said dissolving plug and said flowrestrictor control aqueous flow between one of said first and secondsurfaces of said elastomeric plate and said eye.
 4. An implant fordraining aqueous fluid from an eye, comprising:a thin, elastomeric platehaving first and second surfaces joined at the plate perimeter, saidperimeter of said plate being elliptical, said first and second surfacescurved spherically to conform to the curvature of said eye; and anelastomeric drainage tube attached to said plate, said drainage tubecomprising a first end and a second end, said first end open onto one ofsaid first and second surfaces of said elastomeric plate and whereinsaid second end extends for connection with said eye to provide fluidcommunication between said eye and said one of said first and secondsurfaces of said elastomeric plate, wherein said drainage tube comprisesfirst and second drainage tubes, said first drainage tube having adissolving plug positioned therein, said second drainage tube having aflow restrictor positioned therein, wherein said dissolving plug andsaid flow restrictor control aqueous flow between one of said first andsecond surfaces of said elastomeric plate and said eye, wherein saiddissolving plug is formed of PVA, PVP, or collagen.
 5. An implant fordraining aqueous fluid from an eye, comprising:a thin, elastomeric platehaving first and second surfaces joined at the plate perimeter, saidperimeter of said plate being elliptical, said first and second surfacescurved spherically to conform to the curvature of said eye; and anelastomeric drainage tube attached to said plate, said drainage tubecomprising a first end and a second end, said first end open onto one ofsaid first and second surfaces of said elastomeric plate and whereinsaid second end extends for connection with said eye to provide fluidcommunication between said eye and said one of said first and secondsurfaces of said elastomeric plate, wherein said drainage tube comprisesfirst and second drainage tubes, said first drainage tube secured with aligature, said second drainage tube having a flow restrictor positionedtherein, wherein said ligature and said flow restrictor control aqueousflow between one of said first and second surfaces of said elastomericplate and said eye to control flow between one of said first and secondsurfaces of said elastomeric plate and said eye.
 6. A method ofinserting an implant into an eye for treatment of glaucoma, said implantcomprising an elastomeric plate attached to an elastomeric drainagetube, comprising the steps of:making an incision in the Tenon's capsuleof said eye; folding said elastomeric plate to reduce its size;inserting said folded elastomeric plate into said incision; releasingsaid folded elastomeric plate such that said plate returns to itsoriginal configuration; positioning said plate over the sclera of saideye beneath said Tenon's capsule; and positioning said drainage tubewithin said eye so as to provide fluid communication between said eyeand said elastomeric plate.
 7. The method of claim 6, further comprisingthe step of suturing said elastomeric plate to the sclera of said eye tosecure said implant to said eye.
 8. The method of claim 6, wherein thestep of positioning said drainage tube within said eye comprises placingsaid drainage tube in said anterior chamber of said eye.
 9. The methodof claim 6, further comprising the step of ligating said drainage tubeso as to prevent initial aqueous flow through said drainage tube.